A photoresist resin used in a step of producing a semi-conductor is demanded to have a property allowing a part exposed by light-irradiation to change to alkali soluble, substrate adhesion to a silicon wafer (a base), plasma-etching resistance, transparency for used light at same time. The photoresist resin is generally applied as a solution containing a polymer which is a main agent, a photo-acid generator and some additives for adjusting the above properties.
So far, a photoresist resin containing a monomer unit having bridged alicyclic lactone skeleton as a monomer unit providing substrate adhesion and etching resistance has been proposed (for example, Japanese Unexamined Patent Application No. 2000-26446 and Japanese Unexamined Patent Application No. 2000-122294). However, when a semi-conductor is produced by using such a photoresist resin, there are some problems that an insoluble substance for a resist solvent generates in the solution and therefore micro-pattern can not be obtained accurately. It is demanded to repeat a complicated filtrating procedure to obtain micro-pattern accurately.